Islam was taken into custody on the Eastern Metropolitan Bypass, district police superintendent Pravin Tripathi told IANS.

Mollah, a former minister and a senior legislator, was severely beaten up by Trinamool workers led by Islam Jan 6 when he went to Bamanghata area where a Communist Party of India-Marxist (CPI-M) office had been damaged.

Mollah is still in hospital with multiple injuries, including a lumber bone fracture. The attack caused a political uproar, with the civil society expressing concern over the law and order situation.

The disturbances stretched to Jan 8 when a number of political activists were injured in firing and clashes between the Trinamool and CPI-M.

Governor M.K. Narayanan had said: "This is not a good political culture. I think some sort of goondaism is going on here."

The CPI-M called Islam's arrest belated while Trinamool activists took out a protest rally.

CPI-M general secretary Prakash Karat, who called on Mollah at the hospital Thursday, demanded that the law should take its full course to ensure justice.

"We have been demanding for nearly two weeks that those responsible for the attack on Mollah should be arrested. Today one of the main persons has been arrested. This is only the first step, a beginning," he said.

"We want the law to take its full course. Justice should be done. We will see if it (the arrest) is being followed up," he said.

Former CPI-M MP Sujon Chakraborty, now secretary of the party's South 24 Parganas district, said the government should have taken action against Islam earlier.

"We had to fight. All over the state people were disturbed. But if Arabul is released after two-three days, then we have to say this is only an eyewash," he said.

Enraged after the arrest, Trinamool activists hit the streets at Bhangor district where shops downed shutters. Additional police forces were rushed to prevent violence.